This invention relates to a fan, and more specifically, to the structure of a fan particularly suited for use with electro-machinery.
Electro-machinery such as an electric motor generates a sizeable amount of internal heat during operation, and it is common practice to provide the motor with a cooling fan. A fan is mounted on the motor drive shaft, and the fan turns with the shaft during operation and produces cooling air flow around the motor. One particular type of motor is referred to in the trade as a Totally Enclosed Fan Cooled (TEFC) motor, and it includes a fan mounted on the rotor shaft outside the motor housing or shell. The fan causes cooling air to flow around external cooling fins formed on the motor housing. The fan is typically made of a high strength plastic, and is produced by an injection molding process.
A problem encountered in the manufacture of an injection molded fan is that the molds are quite expensive for the fan of a large size motor. Such a fan may have an outer diameter between one-two feet, for example. Since the cost of a mold increases approximately with the cube of its size, it will be apparent that the cost of a mold for a large one-piece fan may be quite high. This problem of relatively high cost of molding large parts is often exacerbated by the relatively low volume of large parts. If the volume is at least, for example, 10,000 to 15,000 parts per year, injection molding is economically feasible, but a low volume, large size part may be excessively expensive to produce when molding prior art designs for large motors.
It is a general object of the present invention to provide an improved fan design which may be economically manufactured by injection molding, in a variety of sizes.